The present invention relates to measurement of relevant properties of longitudinally air permeable rods, for example, cigarette rods, filter cigarette rods and filter rods and the like.
In order to monitor and maintain standards in mass produced smoking articles, such as cigarettes, filter cigarettes and filter rods, sample articles are taken from the production run and analysed. Important parameters that are measured include the pressure drop (or resistance to draw) weight, size and ventilation.
Conventionally, such properties are measured using fully automated testing machines. It is necessary to check that these machines are measuring correctly.
Conventionally, test machines have been checked using recognised standards. These are instrument specific and, being glass, are expensive and breakable. Known measurement check rods are not satisfactory as they have poor air flow properties which lead to unreliable pressure and ventilation results.